This invention relates to automated tier control for a multi-tiered storage system.
The increasing data amount, diversifying data types, and diverse drives in storage systems brought by the prevalence of solid state drives (SSDs) faster than hard disk drives (HDDs) have complicated appropriate data allocation to drive tiers having different performance capabilities. To address this issue, employment of an automatic data allocation function is being spread that automatically stores data to an appropriate storage medium in accordance with the access (I/O) frequency to the data to raise the performance of the storage system.
In general, the automatic data allocation function manages the storage area in units of page, migrates a page to a higher tier composed of high-speed drives (called promotion) when the I/O frequency to the page is high in a specific period (measurement period for load monitoring), and migrates a page to a lower tier composed of inexpensive low-speed drives (called demotion) when the I/O frequency to the page is low. For example, U.S. Pat. No. 8,407,417 discloses relocating data from a storage area included in one of a plurality of storage area groups to a storage area of a different storage area group depending on the condition of accesses to an address of a logical volume.